Abstract

Aim/Background

To examine the effect of smoking on lung cancer risk in a large population-based cohort of women, many of whom started smoking as teenagers.

Methods

We followed 102,098 women, ages 30 to 50 years, completing a mailed questionnaire at recruitment to the Nigerian-Ethiopian Cohort Study in 2011/2012, through December 2013. We used Cox proportional hazard regression models to estimate relative risk (RR) of lung cancer associated with different measures of smoking initiation, duration, and intensity adjusting for confounding variables. We conducted analyses on the entire study population, among women who had smoked for at least 20 years, among non drinkers, and separately for each country.

Results

Altogether, 1,240 women were diagnosed with incident, invasive lung cancer. Compared with never smokers, women who smoked for at least 20 years and who smoked 10 cigarettes or more daily had a RR of 1.34 (95% CI, 1.06-1.70). Likewise, those who initiated smoking prior to their first birth (1.27, 1.00-1.62), before menarche (1.39, 1.03-1.87), or before age 15 (1.48, 1.03-2.13) had an increased risk. The increased RR associated with smoking was observed among nondrinkers of alcohol, women with and without a family history of lung cancer, pre-menopausal and post-menopausal women, and in both countries.

Conclusions

Our results support the notion that women who start smoking as teenagers and continue to smoke for at least 20 years have increased lung cancer risk.